Generation of variable concentrations of chlorine dioxide

ABSTRACT

A chlorine dioxide generator is provided. The generator includes a controller, a pump electrically connected to the controller and configured to pump reactant feedstock, a power supply electrically connected to the controller, and an electrochemical cell electrically connected to the power supply and configured to receive reactant feedstock from the pump and produce chlorine dioxide. The controller is configured to receive user chlorine dioxide concentration input data and provide control signals to at least one of the pump and power supply to variably control a concentration of chlorine dioxide provided by the electrochemical cell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to chlorine dioxide generators. More particularly, the present invention relates to a chlorine dioxide generator that produces variable concentrations of a chlorine dioxide solution for use in different applications, including but not limited to water treatment systems.

2. Description of the Related Art

Chlorine dioxide (ClO₂) has many industrial and municipal uses. When produced and handled properly, ClO₂ is an effective and powerful biocide, disinfectant and oxidizer.

ClO₂ is extensively used in the pulp and paper industry as a bleaching agent, but is gaining further support in such areas as disinfection in municipal water treatment. Other applications can include use as a disinfectant in the food and beverage industries, wastewater treatment, industrial water treatment, cleaning and disinfection of medical wastes, textile bleaching, odor control for the rendering industry, circuit board cleansing in the electronics industry, and uses in the oil and gas industry.

In water treatment applications, ClO₂ is primarily used as a disinfectant for surface waters with odor and taste problems. ClO₂ is an effective biocide at low concentrations and over a wide pH range. ClO₂ is desirable because when it reacts with an organism in water, chlorite results, and studies have shown chlorite poses no significant adverse risk to human health. The use of chlorine, on the other hand, can result in the creation of chlorinated organic compounds when treating water. Chlorinated compounds are suspected to increase cancer risk.

Producing ClO₂ gas for use in a chlorine dioxide water treatment process is desirable because there is greater assurance of ClO₂ purity when in the gas phase. ClO₂ is, however, unstable in the gas phase and will readily undergo decomposition into chlorine gas (Cl₂), oxygen gas (O₂), and heat. The high reactivity of ClO₂ generally requires that it be produced and used at the same location. ClO₂ is, however, soluble and stable in an aqueous solution.

ClO₂ can be prepared by a number of ways, generally through a reaction involving either chlorite (ClO₂ ⁻) or chlorate (ClO₃ ⁻) solutions. The ClO₂ created through such a reaction is often refined to generate ClO₂ gas for use in, for example, the water treatment process. The ClO₂ gas is then typically educed into the water selected for treatment. Eduction occurs where the ClO₂ gas, in combination with air, is mixed with the water selected for treatment.

The production of ClO₂ can be accomplished both by electrochemical and reactor-based chemical methods. Electrochemical methods have an advantage of relatively safer operation compared to reactor-based chemical methods. In this regard, electrochemical methods employ only one precursor, namely, a chlorite solution, unlike the multiple precursors that are employed in reactor-based chemical methods. Moreover, in reactor-based chemical methods, the use of concentrated acids and chlorine gas poses a safety concern. Such safety concerns with reactor-based chemical methods are of even greater concern when employed in a confined space, such as in an on-board ship application. A further benefit of electrochemical production of ClO₂ is that the purity of the ClO₂ gas produced is higher than that of reactor-based chemical methods, which tends to have greater amounts of residual chemicals that detract from the ClO₂ gas purity.

Electrochemical cells are capable of carrying out selective oxidation reaction of chlorite to ClO₂. The selective oxidation reaction product is a solution containing ClO₂.

Certain applications can benefit from different concentrations of ClO₂. As an example, in a medical or shipboard application, high quality water is desirable, and high quality water results from high concentration ClO₂. Other applications do not require high concentrations of ClO2, and still other applications require high concentrations under certain conditions and lower concentrations at other times.

Current devices tend to operate using a single concentration setting, i.e. put out ClO2 at a single concentration. It has been very difficult to obtain variable concentration levels of ClO₂ without excessive and complicated and potentially dangerous chemical procedures and devices in place.

Based on the foregoing, it would be advantageous to provide a reliable chlorine dioxide generator that provides ClO₂ at a variable concentration level and overcomes the drawbacks of previously known designs.

SUMMARY OF THE INVENTION

According to one aspect of the present design, there is provided a chlorine dioxide generator including a controller, a pump electrically connected to the controller and configured to pump reactant feedstock, a power supply electrically connected to the controller, and an electrochemical cell electrically connected to the power supply and configured to receive reactant feedstock from the pump and produce chlorine dioxide. The controller is configured to receive user chlorine dioxide concentration input data and provide control signals to at least one of the pump and power supply to variably control a concentration of chlorine dioxide provided by the electrochemical cell. Chlorine dioxide is typically provided to a process, may be provided to a process, where the process may be any type of vehicle, stream, procedure, or otherwise receiving ClO2, including but not limited to a pipe carrying water, a tank, a cooling tower, or an injection well. The chlorine dioxide generator may also include a sensor configured to sense a quantity of chlorine dioxide present in the process. Signals from the sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the sensor.

A storage unit configured to receive chlorine dioxide from the electrochemical cell and maintain the chlorine dioxide may be provided, and the chlorine dioxide generator may also include an alternate sensor fluidly positioned between the storage unit and the process that feeds back concentration values to the controller. The chlorine dioxide generator may include an operator interface terminal configured to receive concentration data and may provide the data to the controller.

Alternately, the present design may include a method for producing chlorine dioxide. The method may include providing a desired concentration value, and based on the desired concentration value, determining an electrical quantity to be provided to a device connected to an electrochemical cell. The method may further include applying the electrical quantity to the device connected to the electrochemical cell, thereby altering performance of the device and altering the concentration of chlorine dioxide provided by the electrochemical cell.

The method may also include distributing chlorine dioxide provided by the electrochemical cell to a process, and monitoring concentration of chlorine dioxide in the process and employing the concentration of chlorine dioxide in the process in determining the electrical quantity. The electrical quantity may be an electrical current, including current amplitude and/or on/off times, and the device a pump configured to pump reactant feedstock to the electrochemical cell, or the electrical quantity may be a voltage and the device a power supply configured to supply current to the electrochemical cell.

These and other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which:

FIG. 1 illustrates a previous chlorine dioxide generator;

FIG. 2 shows certain components in the previous chlorine dioxide generator;

FIG. 3 illustrates the present design including variable control of chlorine dioxide concentration; and

FIG. 4 is a flowchart of overall operation of the present design.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a process flow diagram of an embodiment of a previously available chlorine dioxide solution generator 100. FIGS. 1 and 2 are taken from U.S. Pat. No. 7,799,198, issued Sep. 21, 2010, inventors Chenniah Nanjundiah et al., assigned to the assignee of the present application, the entirety of which is incorporated herein by reference. The process flow of FIG. 1 consists of three sub-processes including an anolyte loop 102, a catholyte loop 104 and an absorption loop 106. The anolyte loop 102 can produce a ClO₂ gas by oxidation of chlorite, and the process in combination with catholyte loop 104 can more generally be referred to as a ClO₂ gas generator loop. The ClO₂ gas generator loop is essentially a ClO₂ gas source. Catholyte loop 104 of the ClO₂ gas generator loop produces sodium hydroxide and hydrogen gas by reduction of water. Once the ClO₂ gas is produced in the ClO₂ gas generator loop, the ClO₂ gas is transferred to absorption loop 106 where the gas is further conditioned for water treatment end-uses. The process can be operated through a program logic control (PLC) system 108 that can include visual and/or audible displays.

In this application, the term “absorb” refers to the process of dissolving or infusing a gaseous constituent into a liquid, optionally using pressure to affect the dissolution or infusion. Here, ClO₂ gas, produced in the ClO₂ gas generator loop, is “absorbed” (that is, dissolved or infused) into an aqueous liquid stream directed through absorption loop 106.

While various components are shown in FIG. 1, including a soft water source, blower, stripper column, byproduct tank, and so forth, many of these devices are not pertinent or are optional in the present situation. Note, however, that reactant feedstock is pumped into anolyte loop 102 and passes to an electrochemical cell positioned within anolyte loop 102 and catholyte loop 104, and ClO₂ solution is provided from the absorber tank in absorption loop 108.

FIG. 2 illustrates the anolyte loop 102 that may be employed in chlorine dioxide solution generator 100. The contribution of anolyte loop 102 to the ClO₂ solution generator is to produce a ClO₂ gas that is directed to absorption loop 106 for further processing. The anolyte loop 102 embodiment illustrated in FIG. 2 is for producing a ClO₂ gas using a reactant feedstock 202.

The reactant feedstock 202 can be connected to a chemical metering pump 204, which delivers the reactant feedstock 202 to a recirculating connection 206 in the anolyte loop 102. Recirculating connection 206 in anolyte loop connects a stripper column 208 to an electrochemical cell 210. The delivery of the reactant feedstock 202 can be controlled using PLC system 108. PLC system 108 can be used to activate chemical metering pump 204 according to signals received from a sensor 212. Sensor 212 is generally located along recirculating connection 206 and measures an amount of ClO₂ in the stream, typically as a percentage, but any type of senor that can sense an absolute or relative quantity of ClO₂ may be employed. A sensor set point can be established in PLC system 108, and once the set point is reached, the delivery of reactant feedstock 202 can either start or stop. Such “start and stop” delivery of reactant feedstock has been typical of previous designs.

Reactant feedstock 202 can be delivered to a positive end 214 of electrochemical cell 210 where the reactant feedstock is oxidized to form a ClO₂ gas, which is then dissolved in an electrolyte solution along with other side products.

In this design, the ClO₂ solution with the side products is directed away from electrochemical cell 210 to the top of stripper column 208 where a pure ClO₂ is stripped off in a gaseous form from the other side products. Side products or byproducts can include chlorine, chlorates, chlorites and/or oxygen. Pure ClO₂ gas is then removed from stripper column 208 under a vacuum induced by gas transfer pump 216, or analogous gas or fluid transfer device (such as, for example, other vacuum-based devices), where it is delivered to adsorption loop 106. The remaining solution is collected at the base of stripper column 208 and recirculated back across the pH sensor 212 where additional reactant feedstock 202 can be added. The process with the reactant feedstock and/or recirculation solution being delivered into positive end 214 of electrochemical cell 210 can then be repeated.

Modifications to the anolyte loop process can be made. As an example, an anolyte hold tank can be used in place of a stripper column. In such a case, an inert gas or air can be blown over the surface or through the solution to separate the ClO₂ gas from the anolyte. As another example, chlorate can be reduced to produce ClO₂ in a catholyte loop instead of chlorite. The ClO₂ gas is then similarly transferred to the absorption loop 106.

FIG. 3 illustrates the present design, including certain components similar to the design presented in FIGS. 1 and 2. From FIG. 3, operator interface terminal (OIT) 301 enables an operator to select a desired value, such as parts per million of ClO₂ to be provided in a particular application. The value entered may be any quantity, but in the present design generally represents or correlates to the amount or concentration of ClO₂ to be distributed into a stream or supply. The operator interface terminal 301 may be any standard interface terminal that provides the operator with the ability to input a desired setting, even if the desired setting is binary, i.e. increase or decrease from current state. Digital or analog functionality may be employed. One application is an operator interface terminal that provides a digital readout of current concentration and allows the user to increase or decrease concentration of ClO₂ by a desired amount, such as by typing in a desired amount on a keyboard. OIT 301 may be a device such as a personal computer, smartphone, tablet, or other control device.

Electronic signals representing the operator's desired value may be transmitted from operator interface terminal 301 to programmable logic controller (PLC) 302. Signals may be transmitted in any form, including wirelessly, using any number of intermediate devices or a simple wire. The signals transmitted represent the value of concentration requested. PLC 302 transmits signals to chemical feed pump 303 and power supply 304.

Chemical feed pump 303 in the present design provides sodium chlorite (NaClO₂). Again, other chemicals may be employed, but in the production of ClO₂, NaCLO₂ is typically employed. As an example, a 25 percent by weight NaClO₂ solution can be used as the reactant feedstock. Feedstock concentrations ranging from zero percent to a maximum solubility (40 percent at 17 degrees Celsius), or other suitable method of injecting suitable electrolytes, can be employed.

In one embodiment, PLC 302 may alter the amplitude of the electrical current or may vary the on and/or off time of current supplied to chemical feed pump 303, wherein altering current amplitude or varying the on and/or off time of current applied may cause the chemical feed pump 303 to pump reactant feedstock faster or slower. In an instance where a decrease in concentration is desired, pumping less reactant feedstock, or pumping reactant feedstock at a lower rate of speed, may be beneficial. PLC 302 may alter the voltage applied to power supply 304, where altering the voltage results in the power supply 304 applying a different current to electrochemical cell 305, or alternately may vary the on time and/or off time of current applied.

Electrochemical cell 305 receives chemicals from chemical feed pump 303 and current from power supply 304 and outputs ClO₂. Various implementations of electrochemical cells may be employed. In one embodiment, reactant feedstock is delivered to a positive end of the electrochemical cell 305. The reactant feedstock is oxidized to form a ClO₂ gas, and the ClO₂ gas is dissolved in an electrolyte solution along with other side products. The ClO₂ solution with the side products is directed out of the electrochemical cell 305 to absorber tank or column 306, which in essence holds the ClO₂ for later use.

Examples of electrochemical/electrolytic cells may be found in, for example, U.S. Pat. Nos. 5,427,658, 5,458,743, and 5,736,016, but several electrochemical cells exist and may be employed. In general, an electrochemical cell that receives reactant feedstock and electricity and produces ClO₂ may potentially be used in the present design.

The altering of voltage applied to power supply 304 and altering of current sent to chemical feed pump 303 or altering the on and/or off time of current provided to chemical feed pump 303 results in altered current being provided from the power supply 304 to the electrochemical cell 305, as well as an altered quantity of reactant feedstock being provided to the electrochemical cell 305. As a result, the fluid being transmitted from electrochemical cell 305 to absorber column 306 may vary in concentration, namely within a range of parts per million, from a low value to a high value. Thus the chemical maintained in absorber column 306 may vary in concentration at different times during operation based on the concentration of ClO₂ previously provided.

Distribution pump 307 may distribute the ClO₂ in its existing concentration to a process 308. Process 308 may be any type of vehicle, stream, procedure, or otherwise receiving ClO2, including but not limited to a pipe carrying water, a tank, a cooling tower, or an injection well, where typically some type of chemical, such as water, is present or passes through. Sensors can be employed, such as sensor 309, to determine the actual concentration of the ClO₂ in the process. In one arrangement, sensor 309 is placed a distance downstream from the point where ClO₂ is injected into the processing device. The sensor may provide signals back to PLC 302, and these signals may be used by the PLC 302 to alter output current and/or voltage.

Alternate sensor 310 is optional and is attached between distribution pump 307 and process 308. Such an alternate sensor may also provide signals to PLC 302 for purposes of altering the current and/or voltage supplied. Alternate sensor 310 positioned between distribution pump 307 and process 308 provides the actual concentration of ClO₂ being placed into the process 308. Such a sensor may be useful when the absorber column 306 holds a certain amount of ClO₂ at an existing concentration, and the operator seeks a different concentration provided to process 308. A lag in achieving the desired concentration at sensor 309 may occur, and using alternate sensor 310, this lag may be addressed to the extent possible by the PLC 302.

For example, if a specific relatively high concentration is desired, and the alternate sensor 310 shows that a low concentration is coming from absorber column 306, PLC 302 may command a maximum output for a period of time. So that the concentration does not overshoot the desired value set by the operator, the PLC 302 may slowly increase concentration rather than providing maximum concentration, while monitoring concentration using the both sensor 309 and alternate sensor 310. In this manner, using two sensors, one at the process and another after the distribution pump, an accurate concentration may be achieved and maintained. Such control may require an algorithm that compensates for delays in the system, such as the delay needed to change the concentration of ClO₂ being maintained in the absorber column 306.

While certain devices shown in FIG. 3 are shown as single devices, it is to be understood that multiple such devices may be employed, in virtually any combination. As an example, multiple chemical feed pumps may be provided, as well as multiple chemical cells, multiple power supplies, multiple absorber columns, and ClO₂ may be provided to multiple processes. Further, multiple sensors may be employed.

An example of variable concentration operation is provided in FIG. 4. From FIG. 4, point 401 indicates the user sets the desired concentration value at operator interface terminal 301. At point 402, PLC 302 calculates an appropriate current or determines an appropriate on and/or off time for chemical feed pump 303 and an appropriate voltage to be applied to power supply 305. At point 403, PLC 302 applies appropriate voltage(s) and current(s) to the other components, such as chemical feed pump 303 and power supply 305, based on the value input to the operator interface terminal.

At point 404, electricity is provided by power supply 305 and reactant feedstock by chemical feed pump 303 to the electrochemical cell. At point 405, the electrochemical cell provides ClO₂ to a storage unit such as absorber tank 306, and at point 406 a distribution pump 307 distributes the ClO₂ to process 308. Point 407 senses quality of ClO₂ and/or the quality in the process 308, and feeds back values to PLC 302. At point 408, PLC 302 computes necessary changes based on values fed back and alters current(s) and/or voltage(s) accordingly. Again, if a higher concentration of ClO₂ is needed, the PLC may increase voltage to the power supply and/or current to the pump to increase concentration. The operation may continue in the loop as shown until desired operation is attained, different values encountered, or the device is turned off.

Thus the design may include a chlorine dioxide generator including a controller, a pump electrically connected to the controller and configured to pump reactant feedstock, a power supply electrically connected to the controller, and an electrochemical cell electrically connected to the power supply and configured to receive reactant feedstock from the pump and produce chlorine dioxide. The controller is configured to receive user chlorine dioxide concentration input data and provide control signals to at least one of the pump and power supply to variably control a concentration of chlorine dioxide provided by the electrochemical cell. Chlorine dioxide may be provided to a process, the chlorine dioxide generator also including a sensor configured to sense a quantity of chlorine dioxide present in the process. Signals from the sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the sensor.

A storage unit configured to receive chlorine dioxide from the electrochemical cell and maintain the chlorine dioxide may be provided, and the chlorine dioxide generator may also include an alternate sensor fluidly positioned between the storage unit and the process that feeds back concentration values to the controller. The chlorine dioxide generator may include an operator interface terminal configured to receive concentration data and provide signals reflecting the concentration data to the controller.

Alternately, the present design may include a method for producing chlorine dioxide. The method may include providing a desired concentration value, and based on the desired concentration value, determining an electrical quantity to be provided to a device connected to an electrochemical cell. The method may further include applying the electrical quantity to the device connected to the electrochemical cell, thereby altering performance of the device and altering the concentration of chlorine dioxide provided by the electrochemical cell.

The method may also include distributing chlorine dioxide provided by the electrochemical cell to a process, and monitoring concentration of chlorine dioxide in the processing device and employing the concentration of chlorine dioxide in the process in determining the electrical quantity. The electrical quantity may be an electrical current, and the device a pump configured to pump reactant feedstock to the electrochemical cell, or the electrical quantity may be a voltage and the device a power supply configured to supply current to the electrochemical cell.

The design presented herein and the specific aspects illustrated are meant not to be limiting, but may include alternate components while still incorporating the teachings and benefits of the invention. While the invention has thus been described in connection with specific embodiments thereof, it will be understood that the invention is capable of alternate embodiments or further modifications. This application is intended to cover any variations, uses or adaptations of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known and customary practice within the art to which the invention pertains.

The foregoing description of specific embodiments reveals the general nature of the disclosure sufficiently that others can, by applying current knowledge, readily modify and/or adapt the system and method for various applications without departing from the general concept. Therefore, such adaptations and modifications are within the meaning and range of equivalents of the disclosed embodiments. The phraseology or terminology employed herein is for the purpose of description and not of limitation. 

What is claimed is:
 1. A chlorine dioxide generator, comprising: a controller; a pump electrically connected to the controller, the pump configured to pump reactant feedstock; a power supply electrically connected to the controller; and an electrochemical cell electrically connected to the power supply and configured to receive reactant feedstock from the pump and produce chlorine dioxide; wherein the controller is configured to receive user chlorine dioxide concentration input data and provide control signals to at least one of the pump and power supply to variably control a concentration of chlorine dioxide provided by the electrochemical cell.
 2. The chlorine dioxide generator of claim 1, wherein the chlorine dioxide is provided to a process, the chlorine dioxide generator further comprising a sensor configured to sense a quantity of chlorine dioxide present in the process.
 3. The chlorine dioxide generator of claim 2, wherein signals from the sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the sensor.
 4. The chlorine dioxide generator of claim 1, further comprising a storage unit configured to receive chlorine dioxide from the electrochemical cell and maintain the chlorine dioxide.
 5. The chlorine dioxide generator of claim 4, wherein the chlorine dioxide is provided to a process, the chlorine dioxide generator further comprising an alternate sensor fluidly positioned between the storage unit and the process.
 6. The chlorine dioxide generator of claim 5, wherein signals from the alternate sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the alternate sensor.
 7. The chlorine dioxide generator of claim 6, further comprising a sensor configured to sense a quantity of chlorine dioxide present in the process.
 8. The chlorine dioxide generator of claim 7, wherein signals from the sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the sensor.
 9. The chlorine dioxide generator of claim 1, further comprising an operator interface terminal configured to receive concentration data and provide signals reflecting the concentration data to the controller.
 10. The chlorine dioxide generator of claim 1, wherein the controller is configured to selectively apply variable current to the pump.
 11. The chlorine dioxide generator of claim 10, wherein the controller is further configured to selectively apply variable voltage to the power supply, resulting in the power supply providing variable current to the electrochemical cell.
 12. A chlorine dioxide generator, comprising: a pump configured to pump reactant feedstock; a power supply; an electrochemical cell electrically connected to the power supply and configured to receive reactant feedstock from the pump and produce chlorine dioxide; and a controller electrically connected to the pump and the power supply, the controller configured to receive user chlorine dioxide concentration input data and provide at least one of: variable voltage to the power supply; variable current amplitude to the pump; and variable current timing of current to the pump; to vary a concentration of chlorine dioxide provided by the electrochemical cell.
 13. The chlorine dioxide generator of claim 12, wherein the chlorine dioxide is provided to a process, the chlorine dioxide generator further comprising a sensor configured to sense a quantity of chlorine dioxide present in the process.
 14. The chlorine dioxide generator of claim 13, wherein signals from the sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the sensor.
 15. The chlorine dioxide generator of claim 12, further comprising a storage unit configured to receive chlorine dioxide from the electrochemical cell and maintain the chlorine dioxide.
 16. The chlorine dioxide generator of claim 15, wherein the chlorine dioxide is provided to a process, the chlorine dioxide generator further comprising an alternate sensor fluidly positioned between the storage unit and the process.
 17. The chlorine dioxide generator of claim 16, wherein signals from the alternate sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the alternate sensor.
 18. The chlorine dioxide generator of claim 17, further comprising a sensor configured to sense a quantity of chlorine dioxide present in the process.
 19. The chlorine dioxide generator of claim 18, wherein signals from the sensor are fed back to the controller, and the controller is configured to provide control signals based on the signals from the sensor.
 20. The chlorine dioxide generator of claim 12, further comprising an operator interface terminal configured to receive concentration data and provide signals reflecting the concentration data to the controller.
 21. The chlorine dioxide generator of claim 12, wherein the controller is configured to selectively apply variable current to the pump.
 22. The chlorine dioxide generator of claim 21, wherein the controller is further configured to selectively apply variable voltage to the power supply, resulting in the power supply providing variable current to the electrochemical cell.
 23. A method for producing chlorine dioxide, comprising: providing a desired concentration value; based on the desired concentration value, determining an electrical quantity to be provided to a device connected to an electrochemical cell; and applying the electrical quantity to the device connected to the electrochemical cell, thereby altering performance of the device and altering the concentration of chlorine dioxide provided by the electrochemical cell.
 24. The method of claim 23, further comprising: distributing chlorine dioxide provided by the electrochemical cell to a process; and monitoring concentration of chlorine dioxide in the processing device and employing the concentration of chlorine dioxide in the process in determining the electrical quantity.
 25. The method of claim 23, wherein the electrical quantity comprises electrical current and the device comprises a pump configured to pump reactant feedstock to the electrochemical cell.
 26. The method of claim 23, wherein the electrical quantity comprises a voltage and the device comprises a power supply configured to supply current to the electrochemical cell. 